Role of electronic correlations in the Fermi surface formation of Na (x) CoO(2)

Band structure of metallic sodium cobaltate Na (x) CoO(2) (x = 0.33, 0.48, 0.61, 0.72) has been investigated by local density approximation + Hubbard U (LDA+U) method and within Gutzwiller approximation for the Co-t (2g) manifold. Correlation effects being taken into account results in suppression of the e' (g) hole pockets at the Fermi surface in agreement with recent angle-resolved photoemission spectroscopy (ARPES) experiments. In the Gutzwiller approximation the bilayer splitting is significantly reduced due to the correlation effects. The formation of high spin (HS) state in Co d-shell was shown to be very improbable